The prehospital MITI trial is a prospective, randomized, controlled trial to evaluate the practicality, benefit and safety of paramedic administration of thrombolytic therapy and will determine whether thrombolytic therapy initiated in the prehospital setting results in greater preservation of left ventricular myocardium and improved outcome than when therapy is, instead, initiated by physicians and nurses after hospital arrival. The continuation of this project would permit allocation of additional patients in the trial and one-year follow-up (survival, rehospitalization and incidence of reinfarction) in all patients treated in the two strategies. There is consensus that the sooner coronary reperfusion is effected following thrombosis, the greater the clinical benefit. Logistical impediments prevent almost all patients with AMI from receiving thrombolytic therapy in the first hours of AMI; unless it can be administered in the prehospital setting. Patients who meet the prehospital case definition are randomized so that half receive thrombolytic therapy initiated by paramedics prior to hospital arrival; the other half are treated as soon as possible after hospital arrival. Clinical findings, hospital outcome, resultant ejection fraction, myocardial perfusion defect size and long-term (one year) outcome are assessed in both treatment groups.